The present invention, in some embodiments thereof, relates to detection of chemicals and, more particularly, but not exclusively, to devices, systems and methods useful for detecting and identifying explosives.
An ‘explosive’ is a highly energetic, chemically-unstable molecule having a rapid rate of autodecomposition, typically with the accompanying evolution of large amounts of heat and gaseous products. There has been a great increase in the development of low trace and ultra-low trace explosive detection in the last decade, mainly due to the globalization of terrorist acts, clearing of old mine fields, and the reclamation of contaminated land previously used for military purposes.
In addition, the availability of raw materials for the preparation of explosives, together with the growing access to information on preparing these explosives, allows for almost anyone with sufficient will and internet access to prepare an explosive device, known as improvised explosives devices or IED's. The vast number of people passing through borders, public places, airports etc. poses a huge challenge for current day security screening technologies. The same challenge applies to home, and building and critical infrastructure security. The ultimate goal is of course to be able to rapidly and effectively screen every passing person and his belongings, without the need to delay the traffic of people, and without human contact if possible.
Explosives, especially concealed ones, have a very low vapor pressure or ‘signature’ in the surrounding air. The effective vapor pressure of explosives can be reduced by terrorists by a factor of up to 1000, with the use of plastic packages. Detection methods for traces of explosives therefore continue to be plagued by the low volatility of many target analytes.
One of the most commonly-used high explosives over the last 100 years is 2,4,6-trinitrotoluene (TNT), which poses not only a direct security threat, but also great environmental concern due to soil and water contamination near production, storage and test sites.
Analytical procedures in use today for the trace detection of explosives typically involve collecting vapor samples and analyzing them with a sensitive method. Several methodologies have been reported for detecting TNT and other nitro-containing explosives. These are based on electrochemistry, ion-mobility spectrometry, gas chromatography, HPLC, photoluminescence, surface acoustic-wave devices, microcantilevers, fluorescent polymers, surface plasmon resonance, quartz crystal microbalance, immunosensors and other methods. In these existing methods, pre-concentration of air or liquid samples is usually required for a measurable signal to be recorded by the sensor. These procedures are time-consuming, and delay the operation of a sensor. Although some reported methods are very sensitive and selective, most are rather expensive, time-consuming and require bulky equipment, tedious sample preparation and an expert operator. Furthermore, these systems cannot be miniaturized and automated or cannot perform high-throughput analysis.
Table 1 below presents data comparing TNT detection by various currently-employed methodologies.
TABLE 1DetectionDetection MethodLimitremote microelectrode electrochemical sensor in water50ppbluminescent oligo(tetraphenyl)silole nanoparticles20ppbin waterquenching of fluorescence of polymer films in air10ppbelectrochemical detection by carbon nanotubes in5ppbwaterbiochip (on Au) via QCM or SPR in water1-10ppbelectrochemical detection using metallic NP-1ppbCNT composites in wateradsorptive stripping by carbon nanotubes-modified600pptGCE in waterelectrochemical detection by mesoporous SiO2-414pptmodified electrodes in wateroligo(ethylene glycol)-based SPR in water80pptelectrochemical sensing by imprinted electro-46pptpolymerized bis-aniline-cross-linked AuNPs in waterSPR, fabricated dinitrophenylated-keyhole lympet5ppthemocyanin (DNP-KLH) protein conjugate (in water)indirect competitive immunoassay using SPR2ppt(in water)SPR sensing by bis-aniline-cross-linked picric1.2 × 10−3pptacid-imprinted Au-nanoparticles composite in waterIMS (ion mobility spectroscopy) from air and5-10pptwater samplesSAW in water10pptconducting polymers in water20-40pptμ-Electron capture detector100pptAirport sniffers from air samples2000ppt
Specially-trained dogs can detect explosives with the use of their noses which are very sensitive to scents. These dogs are trained by expert handlers to identify the scents of several common explosive materials and notify the handler when they detect one of these scents. While being very effective, the usefulness of such dogs becomes easily degraded when a dog becomes tired or bored, thus limiting their range of application.
Peroxides-based explosives (e.g., cyclic organic peroxides) have also been used recently to build improvised explosive devices, increasing worldwide the awareness thereto. Development of methodologies for the detection of triacetone triperoxide (TATP), hexamethylene triperoxide diamine (HMTD), tetramethylene diperoxide dicarbamide (TMDD) and other cyclic organic peroxides have become an urgent priority. Most organic peroxides are explosive, and some compounds can be easily synthesized by mixing common commercial products such as acetone, hydrogen peroxide and strong acids. Most of the current technology in use for trace detection of explosives is unable to detect peroxide-based explosives [Oxley et al. Propellants, Explosives, Pyrotechnics 34, 539-543 (2009); Önnerud, H., Wallin, S. & Östmark, H. in Intelligence and Security Informatics Conference (EISIC), 2011 European. 238-243 (IEEE)].
Past theoretical studies have showed a plausible approach based on the formation of complexes between the molecular ring structures of cyclic organic peroxide explosives and a central metal moiety, analogous to the formation of clatherates and crown ethers that selectively bind to ionic species in solution. These studies have predicted that TATP molecules can bind to several ions of different valency, with In3+, Zn2+ and Ti4+ showing the highest binding energy [Dubnikova, F., Kosloff, R., Zeiri, Y. & Karpas, Z. The Journal of Physical Chemistry A 106, 4951-4956 (2002)].
Semiconducting nanowires are known to be extremely sensitive to chemical species adsorbed on their surfaces. For a nanowire device, the binding of a charged analyte to the surface of the nanowire leads to a conductance change, or a change in current flowing through the wires. The 1D (one dimensional) nanoscale morphology and the extremely high surface-to-volume ratio make this conductance change to be much greater for nanowire-based sensors versus planar FETs (field-effect transistors), significantly increasing the sensitivity is possible.
Nanowire-based field-effect transistors (NW-FETs) have therefore been recognized in the past decade as powerful potential new sensors for the detection of chemical and biological species. See, for example, Patolsky et al., Analytical Chemistry 78, 4260-4269 (2006); Stern et al., IEEE Transactions on Electron Devices 55, 3119-3130 (2008); Cui et al., Science 293, 1289-1292 (2001); Patolsky et al. Proceedings of the National Academy of Sciences of the United States of America 101, 14017-14022 (2004), all being incorporated by reference as if fully set forth herein.
Recently, extensive work has been carried out with the use of nanowire electrical devices for the simultaneous multiplexed detection of multiple biomolecular species of medical diagnostic relevance, such as DNA and proteins [Zheng et al., Nature Biotechnology 23, 1294-1301 (2005); Timko et al., Nano Lett. 9, 914-918 (2009); Li et al., Nano Lett. 4, 245-247 (2004)].
Generally, in a NW-FET configuration, the gate potential controls the channel conductance for a given source drain voltage (VSD), and modulation of the gate voltage (VGD) changes the measured source-drain current (ISD). For NW sensors operated as FETs, the sensing mechanism is the field-gating effect of charged molecules on the carrier conduction inside the NW. Compared to devices made of micro-sized materials or bulk materials, the enhanced sensitivity of nanodevices is closely related to the reduced dimensions and larger surface/volume ratio. Since most of the biological analyte molecules have intrinsic charges, binding on the nanowire surface can serve as a molecular gate on the semiconducting SiNW [Cui et al., 2001, supra].
U.S. Pat. No. 7,619,290, U.S. Patent Application having publication No. 2010/0022012, and corresponding applications, teach nanoscale devices composed of, inter alia, functionalized nanowires, which can be used as sensors.
Recently, Clavaguera et al. disclosed a method for sub-ppm detection of nerve agents using chemically functionalized silicon nanoribbon field-effect transistors [Clavaguera et al., Angew. Chem. Int. Ed. 2010, 49, 1-5]. McAlpine et al. [J. Am. Chem. Soc. 2008 Jul. 23; 130(29):9583-9] disclosed a scalable and parallel process for transferring hundreds of pre-aligned silicon nanowires onto plastic to yield highly ordered films for low-power sensor chips. The nanowires exhibit parts-per-billion sensitivity to NO2. SiO2 surface chemistries were used to construct a ‘nano-electronic nose’ library, which can distinguish acetone and hexane vapors via distributed responses [Nature Materials Vol. 6, 2007, pp. 379-384].
WO 2011/154939 discloses SiNW-FET devices, chemically-modified with a monolayer of an amine-functionalized silane derivative, which can be efficiently used to detect small amounts of nitro-containing explosives.
Additional background art includes U.S. Patent Application having Publication No. 2010/0325073.